The present invention relates generally to an unloader, and more particularly to improvements in unloaders to unload bulk cargoes such as coal and grain from the holds of ships.
The conventional unloader comprises a travel frame, a slewing table mounted on the travel frame so as to be turnable freely, a boom mounted on the slewing table so as to be swingable up and down freely, a vertically conveying section mounted freely swingably on the front end of the boom, and a screw feeder for scraping and taking in bulk cargo mounted at the bottom of the vertically conveying section. The screw feeder has a cylindrical screw casing and a screw in the screw casing. The screw feeder, rotating the screw, scoops up bulk cargo through the bottom end of the screw casing, carries it upward, and feeds it into a receiving space between the two belts of the vertically conveying section.
The screw comprises a screw shaft, a spiral blade, and paddle-like discharge blades. Directly by the discharge blades, a discharge port for feeding bulk cargo to the receiving space is made in the screw casing.
At the back of the receiving space, a pair of tail pulleys are arranged up and down. The pair of belts are installed on the upper and lower tail pulleys, respectively, and through the vertically conveying section to catch therebetween and carry bulk cargo through the vertically conveying section. The space between and in front of the upper and lower tail pulleys is the receiving space.
Even while a ship is at its moorings, it rocks on the waves, especially on a rough sea in winter, which may cause the bottom of the ship to push up the bottom of the screw feeder. Accordingly, the screw feeder is so mounted on the bottom of the vertically conveying section that it can, when pushed up, move upward relative to the stationary vertically conveying section in order to prevent damage to the unloader.
When the screw feeder is pushed up largely and the discharge blades and the discharge port are raised above the receiving space of the vertically conveying section, the bulk cargo thrown out by the discharge blades does not enter the receiving space, but dashes against the upper tail pulley and scatters outside.
In accordance with the above, an object of the present invention is to provide an unloader wherein bulk cargo can, without fail, be fed from its screw feeder to its vertically conveying section even when the screw feeder is pushed up largely by the rocks of ships.
On the other hand, in case of the conventional unloader, bulk cargo in a ship's hold is carried by a vertical, upward-conveying section inserted in the bulk cargo through a horizontal boom to a downward-conveying section which is connected to the base of the horizontal boom. Then, bulk cargo slides down on a chute through the downward-conveying section onto a discharge conveyor on the ground side. To cope with such large-sized ships as are built in these years, the position of the base of the horizontal boom of such an unloader has to be raised high, which makes large the height difference between the horizontal boom and the discharge conveyor and, hence, the fall of bulk cargo. Therefore, bulk cargo dashes harder upon the discharge conveyor, becoming liable to break, generating larger noises and more dust, and posing a larger risk of damage to the discharge conveyor.
Disclosed in the Japanese Utility Model Publication No. 86940/H5 (1993) is a structure of continuous unloader to reduce shocks, noises, and dust when bulk cargo falls from such a boom conveyor onto such a discharge conveyor. According to the utility model, the second endless belt is so arranged through the downward-conveying section that its carrying surface faces and overlaps the carrying surface of the first endless belt in the downward-conveying section, the first endless belt hanging from the base of the boom. Bulk cargo is caught between the first and second endless belts constituting a double-belt conveyor and carried downward. The bottom (discharging end) of the double-belt conveyor is positioned close to a discharge conveyor on the ground side to make the fall of bulk cargo short.
On the other hand, a continuous loader/unloader of powder and grains is disclosed in the Japanese Unexamined Patent Application No. 267379/H7 (1995). A double-belt conveyor is arranged from the bottom of an upward-conveying section to be hung in the holds of ships, through a horizontal projecting arm, to the bottom of a column-like section on the land side to constitute a twin-belt conveying path of the shape of an upside-down U. Then, the bottom of the conveying path on the land side is brought down to near the upper surface of the quay and extended laterally along the upper surface of the quay, the lower endless belt given a lateral extension longer than that of the upper endless belt. This extra length of the lower endless belt is where powder and grains are discharged and taken in. The projecting arm can turn freely on the column-like section, but the laterally extending portion of the double-belt conveyor along the surface of the quay is stationary. Accordingly, when the projecting arm turns, the downward-conveying portion of the double-belt conveyor is twisted about the vertical axis of the column-like section.
In case of the above continuous unloader of the Japanese Utility Model Publication No. 86940/H5 (1993), bulk cargo is caught between the two endless belts and carried through the downward-conveying section of which the bottom is positioned near the discharge conveyor. Accordingly, the generation of dust at the bulk-cargo receiving portion of the discharge conveyor is reduced. However, because bulk cargo is not covered on the boom conveyor and at the connecting portion between the upward-conveying section and the boom conveyor, dust are generated in such places. Besides, although it is advantageous to make an end pulley the driving pulley in an ordinary belt conveyor, the end pulleys at the bottom of the downward-conveying section of the unloader can not be the driving pulleys, because each of the end pulleys is in the shape of a tsuzumi, or Japanese hand drum, and divided into several pieces side by side on the shaft and each piece is freely journaled. The end pulleys are suitable for closing in bulk cargo between the two belts, but can not be the driving pulleys. Accordingly, a direction-changing pulley adjacent to the belt-tension adjusting mechanism on the return side of each belt and in contact with the carrying surface of the belt is made the driving pulley. Such a driving pulley is liable to slip on the belt due to powdered bulk cargo sticking on the belt surface.
In case of the above continuous loader/unloader of powder and grains of the Japanese Unexamined Patent Application No. 267379/H7 (1995), the bottom portion of the downward-conveying mechanism of the column-like section is fixed onto a gantry, and the horizontal projecting arm (boom) turns on a slewing table on the top of the column-like section. Therefore, the turn of the horizontal projecting arm is limited within the allowable twisting range of the double-belt conveyor in a tubular column of the column-like section. To cope with the twist of the double-belt conveyor in the column-like section, a group of pulleys has to be supported by many horizontal frame structures, of which the bottoms and peripheries have to be supported by rollers supported on flanges of a fixed tubular body. Thus, the whole structure becomes complex, the service lives of the belts are shortened by the twisting, dust is emitted from the gaps between the belts twisted, and considerable dust is generated on the exposed, extra-length part of the lower endless belt laterally extending along the upper surface of the quay.
In accordance with the above, another object of the present invention is to provide an unloader, which is free from the problems mention above, of which the driving pulleys do not slip due to powdered bulk cargo sticking to belt surfaces, over the whole length of which dust is not generated, wherein bulk cargo is not crushed and noises are not generated, and which is not clogged with bulk cargo.
Moreover, continuous loaders to load bulk cargoes carried forward by ground conveyors into the holds of ships are known. Also known are unloaders which can cope with both loading and unloading in accordance with different situations. The superstructure on the base body of this type of unloader can be replaced with a ship loader. The ship loader comprises a turnable boom extending laterally toward the sea, a telescopic chute pivotally mounted on the front end of the boom, and a belt conveyor installed over the lateral boom. Bulk cargo is carried forward by the boom conveyor and slides down on the chute into a ship's hold.
Another type of continuous loader/unloader is disclosed [for example, in the Japanese Utility Model Publication No. 74529/H3 (1991)]. The loader/unloader is a belt conveyor of the shape of an upside-down U comprising a horizontally conveying section and vertically conveying sections on both sides of the horizontal one. A vertical taking-in device comprising a flow conveyor is mounted on a bottom side of a vertically conveying section. An unloader discharge port and a loader discharge port are disposed in the upper and lower portions, respectively, of the taking-in device. The loader discharge port is provided with a lid freely openable and closable. To unload bulk cargo, bulk cargo is taken in by the taking-in device from the unloader discharge port through an unloader hopper and fed to the belt conveyor. To load bulk cargo, bulk cargo carried forward by the belt conveyor running now in the reverse direction is fed into the taking-in device from the loader discharge port through a loader hopper and discharged through the bottom of the taking-in device into a ship's hold. The lid of the loader discharge port is closed while the loader/unloader is unloading bulk cargo.
In case of the above conventional unloader convertible to a loader, it takes many man-hours to change its superstructure between an unloader and a ship loader. In addition, two superstructures have to be provided for each unloader, which costs a lot. In case of the above conventional loader/unloader, because both unloading and loading of bulk cargoes are performed through the taking-in device, its flow conveyor has to be operated not only during unloading but also during loading. Accordingly, it consumes extra power. Bulk cargo is not discharged smoothly while it is loading, and it may be clogged between the taking-in device and the loader discharge port with bulk cargo. Furthermore, it is difficult to discharge a large quantity of bulk cargo at a high speed.
In accordance with the above, still another object of the present invention is to provide an unloader which is free from the conventional problems mentioned above, of which the function can be changed over between loading and unloading by simple operation, which can discharge bulk cargo into the holds of ships easily and smoothly without being clogged and has simple structure, and of which the manufacturing cost is inexpensive.